The present inention relates to a sterilizable composite container as preserving receptacle for food and other filled products and a process for its production.
For the packing of convenience foods, in particular heat-sterilizable convenience foods in preserved form, one-piece containers, trays or multi-compartment trays of steel, aluminum, plastics or laminates of metal and plastic are used. The accompanying lids of these containers or trays are made in each case from the same material as the lower part or from one of the abovementioned materials, the connection of lid and container, tray or lower part taking place by mechanical flanging via a seal by welding or hot sealing.
For this application as long-term preserving pack for food, containers or trays of plastic have the disadvantage, due to the problem of gas permeability of plastics at elevated temperatures, here at temperatures of heat sterilization, of a very complex multi-layered wall consisting of barrier plastics, such as for example ethylene vinyl alcohol (EVAL), polyvinylidene chloride (PVDC), polyacrylates, nitrile plastics or special crystalline polyamides, between polypropylene or polyesters.
Such 0.5 mm-4 mm thick multi-layered constructions of plastics have the disadvantage of an involved, high-cost production process, in particular the shaping. They also have the disadvantage that a recycling of the production waste from the flat sheets and from the formed containers and trays is practically not possible.
Furthermore, these multi-layered plastic trays have to be covered with an aluminum/plastic laminate as only the aluminum ensures the shelf life of the filled product required for preserves of at least six months, due to its absolute barrier effect against the penetration of oxygen.
Flexible laminates from plastic/aluminum/plastic, for example in a thickness of 10-100 .mu.m polyester laminated or coated with 10-100 .mu.m aluminum and 10-100.mu.m polyolefin (polypropylene or polyethylene), are shaped into trays or troughs by stretch forming. These troughs are filled with the foods and sealed with a lid strip of an analogous construction to that of the laminate of the tray, using a vacuum or inert gas flushing. After sterilization, these packs can be stored as preserving receptacles without refrigeration for up to two years.
These described packs of flexible laminates have the disadvantage of low dimensional stability and the tendancy to take on an unattractive appearance due to the formation of folds, in particular if the filled product is viscous or is not intrinsically stable. Furthermore, packs made of these flexible laminates cannot be multi-compartment trays since the intrinsic stability of the troughs is too low, because the laminate does not allow adequately steep partitions between the troughs due to the inferior formability.
The object of the present invention is to develop a composite container which does not have the disadvantages mentioned above and to specify a process for the production of such a composite container.